����ý

Neil Melville would love to explain what weightlessness feels like, but he can’t.

It’s a surprising admission from a man who’s experienced zero gravity more than 1,000 times in his role as a parabolic flight coordinator – where people can be weightless without leaving Earth’s atmosphere – with the European Space Agency. But as he puts it, explaining what happens is like trying to explain the colour red to someone who has never seen it (however, it is, apparently, a little bit like the feeling you get in the moment before the first big drop on a rollercoaster).

One thing Neil, a physics graduate from the University of York, can tell ����ý Bitesize all about is the remarkable effect the absence of gravity can have on everyday objects and actions. Ever wondered what happens if you start crying in space? Read on.

What happens when you strike a match in zero gravity?

The first thing Neil would like to make clear is this - it isn’t advisable to do this on a space station.

The second is that, in zero gravity, things are missing that we perhaps take for granted in regular gravity. With a match flame, it's direction that's lacking.

“Normally,” he said, “when you have a match burning, it’s heating up the air next to it. The flame within is rising, as the cold air gets sucked underneath and replenishes the oxygen. This keeps the flame burning nicely and allows it to retain its shape.”

In zero gravity, there is no up or down. That means the heat generated by the match will not cause the air to rise and isn’t being replenished with fresh oxygen. That also means the match flame will appear dimmer than it would in Earth’s atmosphere. It also burns slower and, perhaps most surprisingly, has a spherical flame.

Neil explained: “The air is diffusing outwards in all directions, instead of going up. It’s less hot as well.”

What happens to a can of fizzy drink in space?

Again, if you do get the invitation to experience weightlessness, don’t upset your hosts by trying this. If you have seen the mess pop can make when it spurts out of a can in everyday life, it’s even worse in space.

Neil said: “[On Earth] you get a pressure build-up in the can, then a pressure release.

“On a space station, you have lower pressure, a little bit like on an aeroplane where crisp packets are hyper-inflated and drinks cans open much more loudly.” This is due to something called Boyle’s law.

It would be far more exaggerated in space than on a plane, so the drink would bubble more strongly. Combine this with a lack of gravity, and opening a can of fizzy drink on a space station would see it gush out and make a huge mess.

“And you’d get in trouble,” Neil added.

What happens when you taste something in zero gravity?

Scientists are still unsure what happens to our taste buds in the lower pressures of space, but people do experience a reduction in taste.

“The fluids in your mouth are flowing differently,” Neil said, which is one thing he thinks might impact flavour. “You’re used to things rolling across your tongue and down, and that doesn’t happen.”

Space travellers also talk of head congestion, as the fluids in the body are not being pulled downwards, as they would be in regular gravity. Neil describes it as the feeling you get with a heavy cold, without actually being ill.

He said: “This reduces the pressure of smell significantly and a large component of taste is that. Reduce your sense of smell and your sense of taste is also compromised.”

One way to counteract a lack of taste is to add more salt to food in the cooking process to bring out the flavour, but this is discouraged on long-term space missions when too much salt would be detrimental to health. Neil explained: “They need to make sure the flavours are quite strong so that the astronauts can taste them properly but they’re getting quite good at it now. They generally report that the food is good.”

Squeezing the moisture from a sponge

In the fizzy drink example, Neil warned about the consequences of fluid in a zero gravity environment.

Squeezing a wet sponge out doesn’t have quite the same chaotic effect, but it will produce an unusual sight.

Neil explained: “Because the water is not going to drip down, it spreads across the available surfaces and the surface tension holds it together.

“Once it comes out of the the sponge, it will form a layer all around it. If it goes on to your hands, it will form a layer all around your hands and it will coat surfaces. If you keep squeezing enough, you will have a film of water all over your hands, and all over the sponge.”

What happens if you sneeze? Or cry?

Sneezing is, as Neil explained, one thing that is not all that different in zero gravity than it is back on Earth.

However, while weightless and floating freely, a particularly strong sneeze can provide enough thrust to make you rotate gently, like a slow-moving Catherine Wheel firework.

Similar to the sponge example, if you are moved to tears while in space, the tears won’t roll down your cheeks as there is no ‘down’. Your eye sockets would instead fill up completely with tears and a good wipe with a tissue or towel would be required to clear them enough for you to see.

You’re flying without wings

Neil’s experience with zero gravity come from what are called parabolic flights. These involve jet planes following an arc-shaped trajectory which provides a brief period of weightlessness as it reaches the top of the arc. Each of these periods is called a parabola.

The trajectory is repeated so passengers can experience these periods of weightlessness multiple times on each flight. As well as being useful in astronaut training, civilians over the age of 18 are able to join the flights. They must pass a medical first and tickets on the France-run flights, where Neil instructs, can cost around 7,000 euros for 15 parabolas of weightlessness.

Neil is used to the experience now. It involves a transition where the flight trajectory sees passengers undergo twice the usual amount of gravity, immediately before entering the period of the weightlessness.

He said: “You only get 20 seconds of zero gravity each time and that’s book-ended by double gravity, on the way up and the way down. Your blood tends to pool in your legs and drains from your head. Then zero gravity comes on over the course of a couple of seconds, you get a rush of blood to the head and an oxygen euphoria for a couple of seconds.

“It’s quite peaceful. It just takes a second or two to relax.”

Just don’t get so relaxed that you crack open a can of pop. You’ll soon get sent down to Earth.

This article was first published in July 2020 and updated in September 2023.